Wind is free, but as anyone who has owned a sailboat can attest, sails will set you back. Nevertheless, wind propulsion may prove to be the most cost-effective way to bring the world’s heavily polluting global shipping fleet into net-zero carbon compliance — a goal the International Chamber of Shipping, which represents virtually all the big players, is committed to reach by 2050.

Does this mean that a new generation of clipper ships is in the works? The golden age of sail redux? There are some romantic souls working on that. But there are also some pragmatic Finns retrofitting freighters and tankers with a century-old mechanical sail technology based on something called the Magnus effect. (A bit more on the physics later.) And at the leading edge of the nearly possible, there are former America’s Cup and Formula One engineers developing wingsailed, almost zero-carbon commercial ships.

Don’t Look Now, But…

The global shipping industry accounts for some 3 percent of CO₂ emissions, almost equal to all the carbon emissions from the entire continent of South America. But while shipping has long been laxly regulated on everything from labor rights to pollution, the industry is beginning to read the writing on the wall.

In July, the UN’s International Maritime Organization adopted a broad strategy to reduce the industry’s greenhouse gas emissions to align with Paris Agreement climate goals, targeting a 40 percent reduction by 2030.

Meanwhile, as noted above, the trade group for the big shippers is promising much more by 2050.

The IMO notes that several of the fuels and technologies needed to put international shipping on track are not yet commercially available. But sails already are.

You read that correctly. As of summer 2021, the number of large vessels with wind propulsion systems installed reached 15. That’s according to the International Windship Association, which expects to add another five by the end of the year and to reach 40 next year. “We now have well over 130 members,” said Gavin Allwright, the association’s secretary. “It’s pretty much inevitable that carbon taxes will come to shipping, so these companies want to be ready.”

Past as Prologue

Picture a new sail freighter, and your mind’s eye might conjure up the EcoClipper500. The EcoClipper500 will be a steel replica of the Dutch clipper ship Noach, built in 1857, provided its organizers can raise the funds to make it a reality. According to Jorne Langelaan, the enterprise’s founder and captain, the 164-year-old design was a practical choice:

“The late 19th century was actually the peak of design of sailing cargo ships. After that, there were, of course, further developments in sailing. But they were all based in yachting, which really means all the design parameters are around as lightweight as possible, and as easy to handle as possible. For sail cargo you want a lot of sail area that is easy to handle, but it needs to propel an enormous weight.”

EcoClipper500 will be nearly 200 feet long, with over 10,000 square feet of sails, and is expected to carry 500 tons of cargo. A life-cycle study conducted by the builders showed that its construction will account for about 1,200 tons of carbon emissions, half generated during production of the steel used, and about a third by steel-fabrication and other shipyard activities.

Now, 1,200 tons may sound like a lot. But spread over an expected life of 50 years, EcoClipper500 would have a carbon footprint of about two grams of CO₂ per ton-kilometer of cargo moved, just one-fifth that of a modern container ship.

Skeptics are still among us. As Low-tech Magazine (yes, that’s a real magazine) noted in a critique of the study, the container ship takes on a great deal more cargo — 50,000 tons versus 500 — and can travel twice as fast. Indeed, some historical clipper ships were far larger than EcoClipper, carrying nearly 8,000 tons. But matching the cost per ton-kilometer of today’s container vessels would be a stretch.

Langelaan may be a romantic, but he’s not a naïf. He has spent years crewing on commercial vessels, both power and sail, and in 2009 co-founded the Fairtransport Foundation. Based in Amsterdam, Fairtransport is in the business of carrying freight on board the Tres Hombres, a sailing ship built in 1943 — and, since 2015, on a second ship, the Nordlys, built in 1873.

“With Tres Hombres, every year there are voyages to Copenhagen with wine cargoes,” Langelaan explained. “The client would pay five cents a bottle for transport by truck. With Tres Hombres, he pays a euro per bottle [20 times as much]. But because he has the story of sail, because it’s zero emissions, his customers pay two or three euros more, so he’s actually making quite a good profit.”

Building in steel seems counterintuitive, as the steel industry itself accounts for a whopping 8 percent of the world’s carbon emissions. Langelaan insists that it is a practical choice, even when the priority is cutting emissions. “Nowadays it’s very hard to find shipyards that are skilled at building large wooden craft,” Langelaan said. “And with steel, we know it will be very easy to scale up” to a larger fleet.

But building in wood is not out of the question. Sail Cargo, a Canadian logistics company, began building Ceiba, a 148-foot wooden topsail schooner, in Costa Rica in 2019. Schooners actually dominated cargo shipping in the latter decades of sailing’s golden age, as they were more maneuverable, required fewer crew and sailed to windward better than the big, square-rigged clipper ships.

n Costa Rica, where nearly all electricity is generated from renewable sources, Ceiba has been hailed as a pilot project for sustainable construction. “Our green shipyard AstilleroVerde quickly became a project in its own right,” the company boasts. “It is a beacon for sustainable wooden shipbuilding, supporting education and training in our coastal community and delivering annual tree-planting programs.”

The builders hope to complete construction of Ceiba and begin commercial operation in 2022. Initial voyages will take the ship northbound to Canada via Hawaii, down past California and home again to Costa Rica. The ship is expected to sail this route twice annually.

One Hundred Years Before the Rotor

As the golden age of sail was nearing its end, a Finnish engineer named Sigurd Savonius invented a new sail technology based on the aforementioned Magnus effect, which exploits the difference in air pressure on opposite sides of a spinning object. Savonius’s sail technology was first demonstrated in 1924 by the German engineer Anton Flettner. Flettner rotors were fitted to two aging schooners and performed well. But they generated little interest until energy use and emissions became priorities. The E-Ship 1, a bizarre-looking, roll-on/roll-off cargo ship launched in 2010 with four Flettner rotors supplementing two diesel engines, is owned by Enercon, one of Germany’s largest commercial wind turbine makers.

The first company to commercialize Flettner rotors was Norsepower, which was founded in Helsinki in 2012. Norsepower has equipped six ships with the rotors, five of them retrofits, one new construction. The company claims a 5--25 percent reduction in fuel usage and emissions, depending on the size and number of rotors that can be installed. Paying customers include Maersk, the Danish freight-hauling giant.

“The typical investment range with our technology is one to four million euros,” said Tuomas Riski, Norsepower’s chief executive. “With today’s energy prices and typical wind conditions, the payback period is from three to nine years. The customer is buying based on return on investment; it is feasible strictly as an investment.”

Riski added that the technology will also complement unproven renewable fuels, such as hydrogen, ammonia or methanol, should these become practical for the shipping fleet: “Those non-fossil fuels will be so expensive, so much more than shipping fuels of today, that we will need to take all measures to minimize consumption. So the business case for our sails only becomes better.”

Just Add Wings

Applying yacht-racing technology to freighters and ferries may not be as wrong-headed as Langelaan suggests. So much money and talent has been thrown at the America’s Cup and other elite sailing events that it would be foolish to ignore their innovations. This year’s America’s Cup yachts reached speeds of 53.4 knots (61.45 mph) — and, even more remarkably, sailed at close to three times the speed of the wind propelling them. Perhaps some of this bleeding-edge technology can be transferred to cargo ships.

That’s the premise behind BAR Technologies — a spin-off from Ben Ainslie Racing (BAR). With a leadership team plucked from successful America’s Cup campaigns and the formidable McClaren Formula 1 motorsports operation, BAR Technologies’ first product for shipping is WindWings: large, solid-wing sails up to 147 feet in height that will be fitted to the deck of bulk cargo ships to supplement conventional power and reduce emissions by as much as 30 percent.

BAR has partnered with Yara Marine Technologies to offer shipping companies bespoke solutions combining WindWings with hull optimization for greater efficiency. The first installation will be a retrofit to a vessel operated by Cargill, the agricultural brokerage colossus, with delivery expected next year.

“Wind is a nearly cost-free fuel at the margin, and the opportunity for reducing emissions alongside significant efficiency gains in vessel operating costs is substantial,” explained John Cooper, BAR’s chief executive. “We’ve invested in our unique wind sail technology to provide vessel owners and operators with an opportunity to realize these efficiencies.”

BAR is primarily about wind-assisted propulsion. An even more ambitious undertaking is Oceanbird, a behemoth automobilecarrying ship being developed by the Swedish companies Wallenius and Alfa Laval. Over 650 feet long, Oceanbird will carry 7,000 cars (Volvos, we trust) and will cross the Atlantic in 12 days, primarily under sail power from five wing sails over 260 feet in height. (They’re telescopic, dropping to a more manageable height to pass under bridges.)

Oceanbird will be a bit slower than a conventional diesel auto-transport, but the energy and emissions reduction is estimated at 90 percent.

Would Volvo’s customers wait a little longer and pay a little more for near-zero carbon transport, like they do for vegan-friendly car interiors? They might. And the fuel savings should offset a bit of the pinch.

“If you take the average container ship’s fuel bill for the year, it’s about $22 million,” said Jay Gardner, president of Wind+Wing technologies, which is also developing wing sails for commercial applications. “With 90 percent of that, Wallenius can pay for a whole lot of added systems.”

Gardner speaks from some experience. Wind+Wing added wing sails to a tourist ferry operated by San Francisco’s Blue and Gold Fleet for a study conducted by the Transportation Sustainability Research Center at the University of California, Berkeley. The pilot project showed a 40 percent decrease in fuel consumption and carbon emissions and would save at least $100,000 on annual fuel costs per vessel. “You can tell people you’re going to save the world,” he said, “but if you do it at twice the cost nobody is going to care.”

Paying for Itself?

In the absence of any peer-reviewed study, nearly all estimates of wind propulsion’s ability to pencil out come from interested parties. That includes people like Allwright of the International Windship Association, who said his own back-of-the-envelope numbers suggest the transition really could pay for itself very rapidly.

“Just with the systems available today, if you put on a generic wind system that doesn’t do anything special, we start to fall into threeto four-year returns on equity,” Allwright said. “If we were to roll out wind propulsion across the fleet this decade to realize a 20 percent savings in fuel, the cost would be about $300 billion. But the savings over the next two decades would be $1 trillion.”

Allwright’s projection might actually be conservative. It doesn’t account for advances in wind- and weather-tracking systems that should steer modern-day ships free of the doldrums that sometimes plagued the clippers. Nor does it factor in the ability to add water turbine generators that could be used to produce green hydrogen in order to power fuel cells and electric motors on calm days.

Believe it or not — and I do believe — the economics of sail power is looking pretty compelling.